Solid state piezoceramic converter with a small output power around 3 watts has been developed and applied as a power source for LCD backlight in notebook computer.
Following references may be referred to understand prior art in this field.
1. C. A. Rosen, "Ceramic transformers and filters", Proc. Electronic Comp. Symp., 1956.
2. H. W. Katz, "Solid state magnetic and dielectric devices", New York: John Wiley and Sons. 1959.
3. W. P. Mason, "Physical acoustics", Vol.1 Part A.1964.
4. R. Holland, "Contour extensional resonant properties of rectangular piezoelectric plates", IEEE Trans., Sonics and Ultrasonics, SU-15. pp. 97-105, April, 1968.
5. A. A. Yerofeev, A. I. Proklin, V. I. Orekhov, et al. "Piezoelectric current transformer", USSR Inventor Certificate No. 1254967, published 1986, Bull. No.32 (in Russian).
However, piezoceramic transformer(PCT) for a large power application was not very successful due to a lack of adequate design of piezoceramic element which can deliver a large output current.
This invention is to design converters using PCT which can directly input household electricity, 220 V (110 V) 50 Hz or 60 Hz at an output power up to several dozens watts for applications such as electric illumination appliances, medical appliances, etc.
Piezoelectric transformer as an electromechanical electric energy transformer has monolithic solid state constructions made of piezoceramic in a form of bar, plate, disk, or cylinder. The unique feature of PCT is the resonance nature of electric energy transfer within a relatively narrow frequency band near the mechanical resonance, where the amplitude of mechanical internal stress achieves the maximum value (1, 2, 3).
While electric energy transfer in traditional electromagnetic (coiled) transformers is realized through electro-magnetic-coupling from the input to the output, energy transfer in a PCT is achieved through electro-mechanical coupling. Unlike a low-impedance electromagnetic transformer, PCT is rather a power source due to a relatively high output impedance.
Piezoceramic transformers have the following major advantages:
enhanced efficiency and a low level of electromagnetic interference PA1 planar construction and highly selective frequency characteristics PA1 simple monolitic construction for ease of mass production PA1 high operating frequency of electric energy transformation PA1 no fire hazard and enhanced safety to shorting
According to the type of deformation wave excited in the bulk of dielectric (piezoelectric) element, PCTs are classified into longitudinally-transverse and bending. The most common PCT are of plate and bar type with excitation of longitudinal oscillations oriented along width, length, or circumference. (4, 5).
Selection of PCT construction and thus its working frequency is determined primarily by the technical requirements to the input and output parameters such as input/output voltage, load resistance, load current, the stability of the output voltage and the admissible driving frequency.